In a small saucepan, add butter and melt over medium. Remove from the heat and allow to cool until it is barely warm to the touch. In a medium bowl, whisk together flour, pecans, sugars, cinnamon, baking powder and salt. Add dry ingredients to the butter and stir just until moistened and crumbly.

To prepare the filling

In a food processor, add pecans, chocolate, sugars and cocoa powder - pulse until the chocolate is finely chopped. Scoop out 1/2 cup and set aside to be used last.

To prepare the batter

In a medium bowl, whisk together flour, baking powder, baking soda and salt.

In a large mixing bowl, beat butter until smooth and creamy. Gradually beat in the sugar and mix until well combined, scraping down the sides as needed. Mix in the eggs, one at a time, beating until each is incorporated before adding the next. Mix in vanilla. Alternately add the dry ingredients and the sour cream, beginning and ending with the dry ingredients.

Spoon about 2 cups of the batter into a 10" tube pan (with removable bottom) coated with nonstick spray, smoothing the top with a spatula. Sprinkle about 1/2 cup of the filling mixture evenly over the batter. Using about another 2 cups of batter, drop dollops all over the top and again smooth the top with a spatula. Scatter another 1/2 cup filling evenly over the batter and cover with 2 more cups batter in the same manner. Layer on another 1/2 cup of filling and then the remaining batter.

Plunge a table knife into the mixture, about 1" from the side of the pan, and run the knife around the pan two times, without lifting up the blade, spacing the circles about 1" apart. Once again, smooth the top with a spatula.

Take a handful of the streusel and squeeze firmly to form a large mass, then break it up into small clumps. Evenly distribute the streusel over the batter. Repeat with the remaining streusel. Clump together the reserved 1/2 cup chocolate filling mixture and scatter on top over the streusel. Lightly press the toppings down into the surface of the cake.

Place into the oven and bake until the top of the cake is golden brown and a skewer place into the center of the cake comes out mostly clean with a few moist crumbs attached, about 70 to 75 minutes. Transfer to a wire rack and let cool for at least an hour before removing from the pan.

Joe,Carole Walter is the king of coffee cakes. She has another similar rippled coffeecake in Fine Cooking magazine, this is with ginger and marcona almonds and it's too-die for:http://www.finecooking.com/recipes/ginger-marcona-almond-coffee-cake.aspx